A/C HELP Needed

[Marcos A]

I have a 90 Silverado and I am trying to get the A/C working for the upcoming Hot Rod Power Tour next month. The truck has the Harrison Compressor (Model # 1131851) and the A/C air inlet valve motor pressure switch (1 wire either gray or white in color) located on the top backside of the compressor is broken. Can that sensor be replaced or does the whole compressor need to be replaced???? I will try to upload of pic.

Any and all help is appreciated.

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[PlayingWithTBI]

That looks like your high pressure shut-off switch. You can replace it (some don't even come with that switch) but then you'll need to evacuate the system and recharge it (you'll loose the charge either way unless you have a recovery system). I'm guessing you're running 134A? If your system is like my 88 C1500 5.7 (I converted it from R12 about 5 years ago) it'll take 20 ounces of the stuff. Depending on how much oil you loose, you'll need up to 8 ounces.

 

[Marcos A]

That looks like your high pressure shut-off switch. You can replace it (some don't even come with that switch) but then you'll need to evacuate the system and recharge it (you'll loose the charge either way unless you have a recovery system). I'm guessing you're running 134A? If your system is like my 88 C1500 5.7 (I converted it from R12 about 5 years ago) it'll take 20 ounces of the stuff. Depending on how much oil you loose, you'll need up to 8 ounces.

Hey. Thanks for the help. Do you happen to have a part number for that part?

So do I need to have this switch or can I run it without it???

I bought the truck used so I am not entirely sure what’s in the system so I will assume it’s the original R12.

How hard is it to convert from R12 to the 134 stuff??


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[studigggs]

That switch is not a high pressure cutoff, it only controls the recirc/blend door operation on 88-90 (AC control heads w/ no max/recirc button). If you dont hook it up you will only have fresh air when using AC. Not a big deal depending on your climate. If you cut off that connector and ground it, your truck AC will switch to recirc after 30s of operation.

 

[PlayingWithTBI]

I bought the truck used so I am not entirely sure what’s in the system so I will assume it’s the original R12.

Look at your fittings on the high and low sides, if they are screw-on you probably still have R12. If they are quick-connect there's a good bet it's been upgraded to 134A.

That switch is not a high pressure cutoff, it only controls the recirc/blend door operation on 88-90 (AC control heads w/ no max/recirc button). If you dont hook it up you will only have fresh air when using AC. Not a big deal depending on your climate. If you cut off that connector and ground it, your truck AC will switch to recirc after 30s of operation.

That's new to me, that would explain why my new compressor didn't come with it and after I put the sensor/switch in and connected/disconnected the wire, the compressor kept running. I just thought the wire going to the ECM connection was bad. How does it work, does it ground the wire when it senses more system pressure?

How hard is it to convert from R12 to the 134 stuff??

Some people cheap out on it, some do it right. The 2 oils are not compatible so the system at least needs to be flushed.

https://originalair.com/converting-to-134a-general-motors

 

[studigggs]

That's new to me, that would explain why my new compressor didn't come with it and after I put the sensor/switch in and connected/disconnected the wire, the compressor kept running. I just thought the wire going to the ECM connection was bad. How does it work, does it ground the wire when it senses more system pressure?

Yep. Just grounds the wire when high side pressure goes over 210. That tells the recirc mode to enable after a 30s delay. Once pressure goes down to 165, the switch opens and you get fresh air again.

Those are the OEM values for r12. If you switch to 134a, you’ll need different switches in both the low side (cycling) and high side (fresh air Door). Four Seasons website lists the pressures for different model numbers. Somewhere in my post history I list the PNs required.

 

[Marcos A]

Yep. Just grounds the wire when high side pressure goes over 210. That tells the recirc mode to enable after a 30s delay. Once pressure goes down to 165, the switch opens and you get fresh air again.

Those are the OEM values for r12. If you switch to 134a, you’ll need different switches in both the low side (cycling) and high side (fresh air Door). Four Seasons website lists the pressures for different model numbers. Somewhere in my post history I list the PNs required.

So wait all I have to do is cut that connector and ground the wire????? And then my A/C will work as “Normal”?????


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[studigggs]

if you ground it you can have recirc A/C. If you want fresh air, either kick the temp selector one notch to the red, move the output to floor, or put it the fan on low speed. All these actions bypass the compressor switch being grounded.

 

[Marcos A]

if you ground it you can have recirc A/C. If you want fresh air, either kick the temp selector one notch to the red, move the output to floor, or put it the fan on low speed. All these actions bypass the compressor switch being grounded.

OK but if look at my picture it looks as if there is a little tube coming out of the compressor (in the picture behind the compressor looks like it has a yellow gasket) - I'm assuming that the tube gets the pressure signal to the wire that you are telling me to ground?? but will that tube leak out Coolant/lose pressure?

I am not sure if there is coolant in the system or not and I want to make sure I account for everything before I go take it to an A/C place to get the system serviced/refilled.

 

[89GMCJOHN]

"Yep. Just grounds the wire when high side pressure goes over 210. That tells the recirc mode to enable after a 30s delay. Once pressure goes down to 165, the switch opens and you get fresh air again."

So dumb question if someone were to ground this wire out permanently on purpose forcing the AC to recirc mode 100% of the time the AC will just work in recirc mode and not overpressurize itself accidently right ? In other words no damage can occur to the system running grounded all the time ?

Im in Florida and would love mine to be on recirc all the time ....any pitfalls here if I ground that wire on purpose ?